The present invention pertains to pneumatic percussion drills of the type in which a drill stem has an impact receiving member which is disposed in blow-receiving relationship with the percussion hammer and the drill includes mechanism for rotating the impact receiving member.
In the art of percussion rock drills and the like the impact receiving member, commonly known as the shank, is supported in a rotatable chuck in a position to be struck by repeated blows of an impact piston hammer. The chuck is mounted in the forward part of the drill housing and is subjected to mechanical and thermal stresses imposed thereon due to the high frequency blows transmitted from the piston hammer through the shank and due to the high thrust forces caused by the forward feeding force transmitted through the chuck to the drill stem.
Not only are the chuck parts and the shank subjected to high stresses but the location of the chuck in the forward part of the drill housing exposes the chuck parts to the drill cuttings being ejected from the drill hole particularly when the drill is in close proximity to the workface or when drilling is being carried out in an upward direction. It is particularly difficult to effectively seal the chuck end from entry of drill cuttings because the shank extends through the end of the housing and undergoes continuous rotary and oscillatory movement during operation of the drill.
It has been proposed to provide lubrication and cooling of the chuck housing and parts by introducing pressure air from the drill motor supply source. Pressurizing the chuck housing with motive air at supply pressure also substantially prevents entry of drill cuttings into the chuck housing. However, this method of treating the chuck end of the drill is somewhat inefficient since high pressure motive air is used directly only for cooling, lubrication, and sealing purposes.